Implement chained subscript operator on Celerity accessors

[n-io]

Hello,

I have the following piece of code:

QueueManager::getInstance().with_master_access([&](celerity::handler& cgh) {
      auto result = output_buf.template get_access<cl::sycl::access::mode::read>(cgh, cl::sycl::range<2>(args.problem_size, args.problem_size));
      
      for (size_t i = 0; i < args.problem_size; i++) {
        for (size_t j = 0; j < args.problem_size; j++) {
          output[i*args.problem_size + j] = result[i][j];
        }
      }

It yields the following error (using a hipSYCL CPU-backend):

/p/project/celerity/code/celerity-bench/single-kernel/sobel.cc:108:51: error: no match for ‘operator[]’ (operand types are ‘celerity::accessor<hipsycl::sycl::vec<float, 4>, 2, (hipsycl::sycl::access::mode)1024, (hipsycl::sycl::access::target)2018>’ and ‘size_t’ {aka ‘long unsigned int’})
           output[i*args.problem_size + j] = result[i][j];
                                                   ^

Using a hipSYCL GPU-backend the error message appears similar:

/data/code/celerity-bench/single-kernel/sobel.cc:108:51: error: no viable overloaded operator[] for type 'celerity::accessor<hipsycl::sycl::vec<float, 4>, 2, hipsycl::sycl::access::mode::read, hipsycl::sycl::access::target::host_buffer>'
          output[i*args.problem_size + j] = result[i][j];
                                            ~~~~~~^~

The code has not changed since the last time I used it successfully on the master branch. Please could you have a look and advise?

Many thanks in advance!

[psalz]

This is because we now return a custom celerity::accessor type from calls to celerity::buffer::get_access, as opposed to simply returning cl::sycl::accessor. Our custom accessor currently doesn't support the "chained subscript operator" for accessing elements, however you can simply use the overload taking a cl::sycl::id instead!

We should implement the chained operator at some point however. I've renamed the issue so we can keep track of this going forward.